Finally stretched out beyond 200yds...

Last weekend, I finally got to stretch my rifle out beyond 200yds. Ringing steel at a third of a mile is super satisfying, and I can't wait to do it again. However, I'm a little confused at my observed dope, and wondered if anyone had ideas on what might be the cause.

I'm shooting a stock Ruger Precision Rifle in 6.5 Creedmoor, and sending Hornady 147gr ELD-M factory loads. On paper at 100 and 200 she was shooting straight and true; as I reached out to steel at longer ranges, it seemed like my calculated dope was increasingly incorrect. For example, at 475 yds, my app calculated 2.7 mils up, but I needed 2.8 to get center hits on the gong. At 550, it was 3.7 mils vs 3.4 calculated, and at 625 it calculated 4.2 mils and actual was somewhere between 4.7 and 5.0 mils - I was having a hard time clearly seeing the plate. 4.2 was definitely sending it into the dirt low.

Obviously there's a theory-to-reality interface that calculation must traverse, but a difference of 0.5 mils at 625yds is almost a foot of extra drop. When there was wind, it was full-value left-to-right, so it's not like I was shooting into a headwind. Is this just to be expected? Thanks all!

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EDIT: as u/SR_Powah and u/distancenewbie pointed out below, my velocity was wrong. Y'all are awesome, thanks!